Control of malaria in Pakistan by applying deltamethrin insecticide to cattle: a community-randomised trial

Background The standard method of malaria control in south Asia, indoor spr aying of houses with residual insecticide, is becoming prohibitively expens ive to implement and new approaches are needed. Since the region's vector m osquitoes feed predominantly on domestic animals and only secondarily on hu man beings, to apply insecticide to surfaces of cattle instead might be mor e costeffective. We aimed to investigate whether domestic livestock treated with deltamethrin (applied by a sponging method) would prove toxic to mosq uitoes and therefore aid in malaria control. Methods Six Afghan refugee settlements in Pakistan were randomly assigned t o one of two groups. In one group livestock were treated with deltamethrin during the malaria transmission seasons of 1995 and 1997, whereas in the ot her group livestock were treated during the 1996 season. Malaria was monito red by passive case detection at village clinics and by cross-sectional sur veillance. Mosquitoes were also monitored. Findings According to clinic records the incidence of malaria caused by Pla smodium falciparum decreased by 56% (95% CI 14-78%) and P vivax by 31% (5-5 0%) in livestock treated villages. Cross-sectional surveys showed comparabl e decreases in parasite prevalence. The density and life expectancy of Anop heles stephensi and A culicifacies populations were reduced in treated vill ages. The efficacy of livestock treatment was similar to that of indoor spr aying but campaign costs were 80% less. When applied in a highly endemic se ttlement, the incidence of falciparum malaria decreased from 280 episodes p er 1000 person-years to nine episodes per 1000 person-years. Interpretations Insecticide treatment of livestock is a costeffective and p romising alternative for south Asia and other regions where primary vectors are zoophilic.